1. Field of the Invention
The present invention relates to a vaned rotary component of a rotary device for heat engines, such as the turbine wheel of a gas turbine or a turbocharger, and a method of manufacturing the same.
2. Description of the Prior Art
Recently, turbine wheels made of a ceramic material having high-temperature strength, such as silicone nitride or silicon carbide, have been employed in heat engines such as gas turbines and turbochargers to improve the thermal efficiency of heat engines through the increase of the operating temperature and to substitute ceramics for rare resources.
As is generally known, a turbine wheel is manufactured by casting a heat-resistant alloy containing nickel and chromium as the principal components. However, the heat-resistance of such metal is not high, and hence the operating temperature of the heat engine provided with the metallic turbine wheel is limited. In order to meet the requirement for the improvement of the thermal efficiency of the heat engine, turbine wheels formed of a ceramic material having high strength and superior to metals in heat-resistance, such as silicon nitride or silicon carbide, have become manufactured through injection molding process or slip casting process.
A ceramic turbine wheel is formed of a dense sintered body through the processes of preparing a fluidized mixture of a pulverized ceramic material and an organic substance or water, injection-molding or casting the fluidized mixture to form a molding having a desired shape, heating the molding to remove the additives including the organic substance or water, and sintering the molding.
The turbine wheel is driven at a high speed by high-temperature gases produced by the combustion of fuel in a combustor or a combustion chamber to produce power. In a turbocharge, for instance, the maximum circumferential speed of the turbine wheel is as high as 600 m/sec. Combustion gases contain minute particles, such as dust contained in the air used for combustion and metal oxide scales flaked off from the inner surface of the combustion gas passage, which collide against the turbine wheel rotating at high speed. With a turbine wheel formed of a metal having high impact resistance, the impact of particles dents only the peripheral portion of the turbine wheel moving at the highest circumferential speed, and hence no significant problem affecting the performance of the turbine wheel is not caused. However, since the ceramic turbine wheel is brittle, the impact of particles on the ceramic turbine wheel causes chipping or tip damages in the peripheral portions of the vanes of the ceramic turbine wheel, whereby the performance of the ceramic turbine wheel is deteriorated.
In order to obviate such problems in the turbocharger, for instance, means for discharging foreign matters contained in the combustion gas supplied to the turbocharger outside the scroll casing is proposed in Japanese Unexamined Patent Publication No. 22025/1985, in which a circumferential foreign matter guiding groove is formed in the inner surface of the scroll casing, and a foreign matter discharging opening is formed at the end of the foreign matter guiding groove, and thereby the foreign matters are guided along the foreign matter guiding groove and are discharged through the foreign matter discharging opening outside the scroll casing. However, this means is unable to eliminate the foreign matters completely so that the turbine wheel will not be damaged by the foreign matters. After all, it has been desired that the strength of the ceramic turbine wheel itself be enhanced.